﻿using System;

namespace block_explorer.NoiseSystem.Nodes
{
    class PerlinBasis : INode
    {
        public PerlinBasis()
        {
            setup();
        }

        public double Value(double x, double y, double z)
        {
            return noise(x, y, z);
        }

        private int[] p;
        private int[] permutation = { 151,160,137,91,90,15,
        131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
        190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
        88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
        77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
        102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
        135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
        5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
        223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
        129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
        251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
        49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
        138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
        };

        private void setup()
        {
            p = new int[512];
            for (int i = 0; i < 256; i++) p[256 + i] = p[i] = permutation[i];
        }

        private double noise(double x, double y, double z)
        {
            int X = (int)Math.Floor(x) & 255,                  // FIND UNIT CUBE THAT
                Y = (int)Math.Floor(y) & 255,                  // CONTAINS POINT.
                Z = (int)Math.Floor(z) & 255;
            x -= Math.Floor(x);                                // FIND RELATIVE X,Y,Z
            y -= Math.Floor(y);                                // OF POINT IN CUBE.
            z -= Math.Floor(z);
            double u = fade(x),                                // COMPUTE FADE CURVES
                    v = fade(y),                                // FOR EACH OF X,Y,Z.
                    w = fade(z);
            int A = p[X] + Y, AA = p[A] + Z, AB = p[A + 1] + Z,      // HASH COORDINATES OF
                B = p[X + 1] + Y, BA = p[B] + Z, BB = p[B + 1] + Z;      // THE 8 CUBE CORNERS,

            return lerp(w, lerp(v, lerp(u, grad(p[AA], x, y, z),  // AND ADD
                                            grad(p[BA], x - 1, y, z)), // BLENDED
                                    lerp(u, grad(p[AB], x, y - 1, z),  // RESULTS
                                            grad(p[BB], x - 1, y - 1, z))),// FROM  8
                            lerp(v, lerp(u, grad(p[AA + 1], x, y, z - 1),  // CORNERS
                                            grad(p[BA + 1], x - 1, y, z - 1)), // OF CUBE
                                    lerp(u, grad(p[AB + 1], x, y - 1, z - 1),
                                            grad(p[BB + 1], x - 1, y - 1, z - 1))));
        }

        private double fade(double t)
        {
            return t * t * t * (t * (t * 6 - 15) + 10);
        }

        private double lerp(double t, double a, double b)
        {
            return a + t * (b - a);
        }

        private double grad(int hash, double x, double y, double z)
        {
            int h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE
            double u = h < 8 ? x : y,                 // INTO 12 GRADIENT DIRECTIONS.
                    v = h < 4 ? y : h == 12 || h == 14 ? x : z;
            return ((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
        }
    }
}
